Cell specialisation & Cell differentiation — AQA GCSE Biology

LESSON 1.02 · MODULE 1 · CELL BIOLOGY

Specialised Cells

The most common error on this topic isn't getting the structure wrong — it's missing the function link. "Sperm has a tail" scores zero. "Sperm has a tail to swim to the egg" scores the mark. In 10 minutes, you'll know all six cells and the feature-function format that scores.

Learning Objectives

By the end of this lesson, you'll be able to:

Name and identify the six specialised cells in the AQA spec — three animal, three plant

Explain how each cell's structure relates to its function using correct feature-function links

Apply the differentiation process — explain how and when cells become specialised

Spec Ref & Paper

Spec 4.1.1.3–4.1.1.4 · Paper 1 · Higher Tier. Specialised cell questions frequently appear as 2–4 mark "explain how the structure is adapted" questions. The feature-function link is the mark every time.

The Six Specialised Cells

The spec lists exactly six cells you must know. Three animal, three plant. Memorise all six — their names, structures, and functions.

Animal Cells (3)

Sperm cell

Reproduction — carries genetic material to the egg

Nerve cell

Carries electrical impulses rapidly over long distances

Muscle cell

Contracts to produce movement

Plant Cells (3)

Root hair cell

Absorbs water and mineral ions from the soil

Xylem cell

Transports water and mineral ions up the plant

Phloem cell

Transports dissolved sugars (translocation)

The Feature-Function Format

Every adaptation answer must follow this structure: [Feature] → [Function link]. Name the structural feature, then explain what it allows the cell to do. No link = no mark.

Sperm Cell

Function: carry genetic material to the egg and fertilise it. Every structural adaptation serves this purpose.

FeatureFunction link

Long tail (flagellum)Propels the sperm cell — to swim towards and reach the egg

Many mitochondria (in midpiece)Release energy by aerobic respiration — to power the tail for swimming

Streamlined headReduces resistance — to move efficiently through the female reproductive tract

Nucleus containing DNACarries the father's genetic material — to fertilise the egg

Nerve Cell (Neurone)

Function: carry electrical impulses rapidly over long distances between different parts of the body.

FeatureFunction link

Long axonCarries impulses over long distances quickly — between distant parts of the body

Branching dendritesConnect to many other nerve cells — allowing signals to be received from multiple sources

Synapses (at axon terminals)Pass signals to the next cell — allowing communication across the network of neurones

Spec Scope

The AQA spec does not require knowledge of the myelin sheath at GCSE. Keep answers to: long axon, dendrites, and axon terminals with their function links.

Muscle Cell

Function: contract to produce movement. Muscle cells are bundled into muscle fibres and can only pull — not push.

FeatureFunction link

Protein fibresSlide past each other — to shorten the cell and produce contraction

Many mitochondriaRelease energy by aerobic respiration — to power repeated contractions

Root Hair Cell

Function: absorb water (by osmosis) and mineral ions (by active transport) from the soil into the plant.

FeatureFunction link

Long root hair extensionGreatly increases surface area — for faster water and mineral ion absorption from the soil

Many mitochondriaRelease energy by aerobic respiration — to power active transport of mineral ions against the concentration gradient

No chloroplastsRoots are underground with no light — photosynthesis cannot occur so chloroplasts are not needed

Large vacuoleMaintains turgor pressure — helps keep the cell firm to support uptake

Xylem & Phloem Cells

These two plant tissues are frequently confused. Xylem = water transport (dead cells). Phloem = sugar transport (living cells). The named process for sugar transport in phloem is translocation — this is the AQA mark-scheme term.

Hollow (no cytoplasm/nucleus) — dead at maturity; water flows freely through the lumen

Lignin-strengthened walls — provides strength and waterproofing ; withstands pressure

No end walls — cells form a continuous open column for water to travel up

Pits in walls — allow water to move sideways into surrounding cells

Sieve plates (perforated end walls) — allow sugar solution to flow between cells

Thin cytoplasm, no nucleus (in sieve tube) — maximises space for sugar flow

Companion cells alongside — contain many mitochondria to release energy for active loading of sugars

Xylem vs Phloem Confusion

Xylem: water + mineral ions — dead cells — lignin walls — no end walls. Phloem: dissolved sugars — living cells — sieve plates — companion cells with mitochondria. These are frequently swapped in exam answers.

Cell Differentiation (Spec 4.1.1.4)

Specialised cells don't start out specialised. They become specialised through a process called differentiation.

CELL DIFFERENTIATION

The process by which a cell changes to become specialised — it acquires different sub-cellular structures to enable it to carry out a specific function.

Animal Cells

Most types of animal cell differentiate at an early stage of development. In mature animals, cell division is mainly restricted to repair and replacement.

Plant Cells

Many types of plant cell retain the ability to differentiate throughout life — not just early in development. This is why plants can grow new structures continuously.

Why Differentiation Matters — The "Importance"

Differentiation allows a multicellular organism to develop specialised cells, tissues, and organs — each adapted to a specific function. Without differentiation, every cell would be identical and unable to perform the complex, coordinated functions that larger organisms need to survive. This is what the spec means by "explain the importance of cell differentiation."

Differentiation vs Specialisation

Differentiation = the process. Specialisation = the outcome. If asked "what process does a cell undergo to become specialised?" — write "differentiation." Mark schemes accept "differentiation" and ignore "specialisation" as the process name.

Worked Example

A diagram shows a leaf cell (cell A) adjacent to a phloem sieve tube. The concentration of dissolved sugars in the phloem sieve tube is higher than in cell A.

Explain how sub-cellular structures in cell A allow dissolved sugars to be moved into the phloem sieve tube.5 MARKS

Pattern — 5-Mark Explain (Multi-Step Chain)

Step 1: Identify the mechanism — sugars move from LOW concentration (cell A) INTO HIGH concentration (phloem). This is against the concentration gradient = active transport.

Step 2: Active transport needs energy → energy comes from aerobic respiration → aerobic respiration happens in mitochondria.

Step 3: Build the chain: mitochondria → aerobic respiration → energy released → powers active transport → against concentration gradient.

1

Cell A contains mitochondria.

2

Mitochondria carry out aerobic respiration, which releases energy. (Never write "produces energy.")

3

The energy is used to move dissolved sugars against the concentration gradient — from the lower concentration in cell A to the higher concentration in the phloem.

4

This movement against a concentration gradient is called active transport.

5

Active transport cannot occur by diffusion (which only moves substances down a gradient) — the energy from respiration is what makes the uphill movement possible.

Examiner Alerts

Three errors that cost marks on this topic across multiple series.

Alert 1 — Feature Without the Function Link

The single most common error. "Sperm cells have a tail" scores zero — it just names a feature. "Sperm cells have a tail to swim to the egg" scores the mark — it links the feature to the function. Every adaptation answer needs both halves.

Alert 2 — Energy Language

For any cell with mitochondria, mark schemes explicitly reject "energy is produced / made / created." Write "mitochondria release energy by aerobic respiration." This applies to sperm cells, muscle cells, root hair cells, and phloem companion cells.

Alert 3 — Xylem and Phloem Swapped

Examiner reports flag this every series. Xylem = water and mineral ions, dead cells, lignin walls. Phloem = dissolved sugars, living cells with companion cells. Writing "xylem carries sugars" or "phloem cells are dead" both score zero.

Common Errors

Pause and screenshot.

✗ Wrong

"Sperm has a tail" — feature only, no function link

✓ Correct

"Sperm has a tail (flagellum) to swim to the egg"

✗ Wrong

"Phloem cells are dead" / "xylem carries sugars"

✓ Correct

Xylem = water (dead). Phloem = sugars (living, with sieve plates)

✗ Wrong

"Root hair cells use photosynthesis to absorb minerals"

✓ Correct

Root hair cells have no chloroplasts — underground, no light, no photosynthesis

✗ Wrong

"Cells specialise" — no mechanism given

✓ Correct

"Cells differentiate, acquiring different sub-cellular structures" — name the process

Three Things to Remember

Three takeaways. You're set for any specialised cell question on Paper 1.

1. Six Cells — Three Animal, Three Plant

Animal: sperm (reproduction), nerve (impulses), muscle (contraction). Plant: root hair (absorption), xylem (water transport), phloem (sugar transport). Memorise all six with their one-line function.

2. Every Adaptation Needs a Function Link

Feature + "to" + function. "Long axon to carry impulses over long distances." "Many mitochondria to release energy for contraction." The second half is the mark — never give the feature alone.

3. Differentiation Is the Process

Cells become specialised through differentiation — acquiring different sub-cellular structures. Animal cells mostly differentiate early; plant cells can differentiate throughout life. "Specialisation" is the outcome, not the process name.

Summary

Feature-Function Links to Memorise

Sperm: tail → swim to egg · many mitochondria → energy for swimming · streamlined head → reduce resistance

Nerve: long axon → carry impulses long distances · dendrites → receive signals from many cells

Muscle: protein filaments → contract and shorten · many mitochondria → energy for contraction

Root hair: long extension → ↑ surface area for absorption · many mitochondria → active transport of minerals · no chloroplasts → underground, no light

Xylem: hollow/dead → water flows freely · lignin walls → strength · no end walls → continuous water column

Phloem: sieve plates → sugar solution flows · companion cells with mitochondria → energy for active loading

Differentiation (Spec 4.1.1.4)

Differentiation = cells acquiring sub-cellular structures to become specialised

Animal cells: differentiate early · in mature animals, division = repair/replacement only

Plant cells: can differentiate throughout life

Next Lesson

Lesson 1.03 — Microscopy. Light vs electron microscopy, the magnification equation (image ÷ real), unit conversions (mm → µm → nm), and standard form calculations.